The invention relates to surface acoustic wave devices, and in particular to an electromagnetic SAW resonator utilized as a rate sensor and position indicator.
Rotation rate sensing through contactless transduction of circulating acoustic and magnetostatic surface waves on a rotating cylindrical surface has been discussed in prior art literature. U.S. Pat. No. 3,909,710 issued Sept. 30, 1975 to Ronald Newburgh et al., entitled Magnetic Surface Wave Rotation Rate Sensor Using the Sagnac Effect discloses a typical device. In the method involved, a cylinder is mounted separately from and rotated with respect to a single transducer. The velocities of the corresponding circulating clockwise (CW) and counterclockwise (CCW) waves launched on the rotating cylinder are unequal in the laboratory frame. Phase differences proportional to rotation rate then develop between these waves when they recombine at the transducer site. However, state-of-the-art acoustic devices based on magnetostatic and piezoelectric transducers operating at frequencies much higher than a megahertz involve transducer-cylinder alignment difficulties and impose critical transducer-propagation surface gap requirements.
Other available rotation rate sensors such as the ring laser measure rate only, are complex, expensive, and have rate sensitivities of no better than 1/2.degree./hour.
There currently exists, therefore, the need for a SAW motion sensing device that measures both rate and position and that is more easily fabricated, less expensive, and has better sensitivity than existing devices. The present invention is directed toward satisfying that need.